1. Field of the Invention
The invention relates to power consumption reduction of an electronic apparatus, and more particularly to power consumption reduction of an electronic apparatus with analog-to-digital converters.
2. Description of the Related Art
Analog-to-digital converters (ADC) are used to convert analog input signals to digital output signals. Because an analog processing circuit has shortcomings of a larger circuit size and higher circuit complexity in comparison with a corresponding digital processing circuit, analog signals of an electronic apparatus are usually converted into digital signals with analog-to-digital converters before being processed by a digital signal processor or a microcontroller.
Optical disk drives also comprise analog-to-digital converters for signal conversion. To access data stored in an optical disk, an optical disk drive projects a laserbeam onto a surface of the optical disk, and photodetectors of a pickup head then detect amplitudes of the laserbeam reflected from the surface to obtain reflection signals. The reflection signals are then processed by a wobble detection circuit to generate a wobble signal. Referring to FIG. 1, a block diagram of a conventional wobble detection circuit 100 of an optical disk drive is shown. Four photodetectors first respectively generates reflection signals A, B, C, and D. A summing block 101 then sums the reflection signals A and D to obtain a signal ADO. Accordingly, a summing block 102 sums the reflection signals B and C to obtain a signal BCO.
Offset cancellation blocks 103 and 104 then remove DC components from the signals ADO and BCO to obtain signals OFF_ADO and OFF_BCO. Low pass filters 105 and 106 then remove noise components from the signals OFF_ADO and OFF_BCO to obtain signals LPF1O and LPF2O. Partial gain amplifiers 107 and 108 then adjust amplitude of the signals LPF1O and LPF2O to obtain signals PGA1O and PGA2O. Analog-to-digital converters 109 and 110 then digitize the signals PGA1O and PGA2O to obtain signals ADC1O and ADC2O. Automatic gain control units 111 and 112 respectively determine gain AGCCON1O and AGCCON2O of the partial gain amplifiers 107 and 108 according to the signals ADC1O and ADC2O.
A subtraction block 117 then subtracts the signal ADC2O from the signal ADC1O to obtain a signal SUBO. The signal SUBO can be further processed to extract wobble information. A low pass filter LPF3 filters out a noise component from the signal SUBO to obtain a signal LPF3O. The signal LPF3O can be directly used to extract phase modulated address information (ADIP). The signal LPF3O is also delivered to a band pass filter 119 which generates a signal BPFO. The signal BPFO can be used to extract channel bit clock information. The signal LPF3O is also delivered to a land pre-pit determining block 120 which generates a signal LPPO. The signal LPPO can be used to extract land prepit address information.
Because portable electronic devices have limited power resource supplied by batteries, power consumption is an important issue for portable electronic devices such as notebook computers, cell phones, and personal digital assistants (PDA). The ordinary electronic devices comprise analog-to-digital converters, power consumption of the electronic devices is reduced if power consumption of the analog-to-digital converters therein is reduced. For example, when power consumption of the analog-to-digital converters 109 and 110 shown in FIG. 1 is reduced, an optical disk drive comprising the analog-to-digital converters 109 and 110 also show reduced power consumption. Thus, an electronic apparatus comprising analog-to-digital converters with adjustable power consumption is required.